1. Field of the Invention
The present invention relates to a shutter for a camera, and particularly to a focal plane shutter of the electromagnetic driving type for a single lens reflex camera.
2. Description of the Prior Art
Generally speaking in an electromagnetically driven shutter, a return running of the shutter blades is effected by electromagnetic power as is running for exposure. This method of operation does not require a mechanical association between the shutter and a mechanical part, and it has the advantage that the structure of a shutter can be made simple. However, if return running is effected by electromagnetic power as mentioned above, power must be supplied from a power source with a small capacity within a camera for the return running. Therefore, the number of picture frames which can be photographed will be halved compared to a case where electromagnetic power is used only for the shutter during running for exposure.
Also, during return running of the shutter, it is necessary to revise the direction of current flow from the direction during running for exposure. Thus it is necessary to provide switching means to switch direction of the driving current thereby increasing production cost.
It has been proposed to provide an electromagnetic driving type shutter of the two way exposure type wherein an exposure is also effected during return running of a shutter. However, this method also requires switching means to change the direction of driving current. Thus lowering of production cost cannot be lowered although saving in power consumption is achieved.